The nice thing about using an external provider is that they most likely won't go down if your network goes down. If you monitor using Spiceworks, which is completely do-able.... if your network goes offline, there's no way to let you know without having a modem or SMS device.

However, there's a large number of providers, redalert.com, etc., who will do just what you're asking for.

I second NAGIOS. If you set it up in your network and have the web interface accessible to the outside world you can view the site and see what is going on. If your site goes down you will not be able to access the web interface, but the server will still be monitoring and you can look at the logs the next day.

If you set something up at your hose (or your boss's house) you can only monitor when the connection is up. That is way I like the NAGIOS server in your network. NAGIOS can be fun to set up, but when it is up and running it works great. We use it to monitor all of our network routers and switches and our windows and linux servers.